Standby time improvements for stations in a wireless network

ABSTRACT

Techniques to improve the standby time of a station in a wireless network are described. An access point may advertise or convey a maximum listen interval and/or an association timeout supported by that access point. A station may operate in a power-save mode and may wake up every listen interval to receive a beacon and any potential traffic for the station. The station may select a suitable listen interval based on the maximum listen interval. The station may be dormant for a longer duration than the listen interval and may become active at least once in every association timeout in order to keep the association with the access point alive. The access point may also send broadcast and multicast traffic that might be of interest to stations in the power-save mode less frequently and using a special indication message.

The present application claims priority to provisional U.S. ApplicationSer. No. 60/779,235, entitled “STANDBY TIME IMPROVEMENTS FOR WLAN,”filed Mar. 3, 2006, and provisional U.S. Application Ser. No.60/779,824, entitled “STANDBY TIME IMPROVEMENTS FOR WLAN,” filed Mar. 7,2006, both assigned to the assignee hereof and incorporated herein byreference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for improving standby time of a station in awireless network.

II. Background

Wireless networks are widely deployed to provide various communicationservices such as voice, video, packet data, broadcast, messaging, etc.These wireless networks may be capable of supporting communication formultiple users by sharing the available network resources. Examples ofsuch networks include wireless local area networks (WLANs), wirelessmetropolitan area networks (WMANs), wireless wide area networks (WWANs),and wireless personal area networks (WPANs). The terms “network” and“system” are often used interchangeably.

A wireless network may include any number of access points (APs) and anynumber of stations (STAs). An access point may act as a coordinator forcommunication with the stations. A station may actively communicate withan access point, may be idle, or may be powered down at any given momentdepending on the data requirements of the station.

Standby time is an important selling point for portable devices that arebattery powered. Current WLAN portable devices tend to have poor standbytime performance in comparison to cellular phones. For example, thestandby time for currently available WLAN Voice-over-IP (VOIP) phonestypically ranges between 40 and 80 hours on batteries similar to thoseused in cellular phones. In comparison, cellular phones may be able toachieve 400 hours of standby time on similar batteries.

IEEE 802.11 is a family of standards developed by The Institute ofElectrical and Electronics Engineers (IEEE) for WLANs. IEEE 802.11defines a method for a station to sleep and thus save power. However,the efficiency of the method is limited for stations desiring very lowpower consumption because of signaling limitations in the standard aswell as limited support by the access points and/or stations.

There is therefore a need in the art for techniques to improve thestandby time of a station in a wireless network.

SUMMARY

Various techniques to improve the standby time of a station in awireless network are described herein. In an aspect, an access pointconveys a maximum listen interval supported by that access point, e.g.,via a beacon or a unicast frame. The maximal listen interval for a givenaccess point indicates the maximal time interval for which a givenstation may sleep when associated with that access point. The listeninterval for a given station indicates how often that station may wakeup to receive the beacon and potential traffic. A station may operate ina power-save mode and may wake up periodically to receive the beacon andany potential traffic for the station. The station may receive themaximum listen interval from an access point and may efficiently selecta suitable listen interval for that station based on the maximum listeninterval supported by the access point, without having to repeatedlynegotiate different listen intervals with the access point. The stationmay also discover the maximum listen interval in other manners, asdescribed below.

In another aspect, an access point conveys its association timeout tostations within its coverage. The association timeout is a duration oftime in which the access point will keep an association for a stationeven when the station shows no activity during this time duration. Thestation may be dormant for longer than its listen interval in order toextend battery life. The station may obtain the association timeout ofthe access point and may ensure to be active at least once in everyassociation timeout in order to keep the association with the accesspoint alive.

In yet another aspect, an access point sends broadcast and multicasttraffic that might be of interest to stations in the power-save mode (orPS-stations) in a manner such that these stations may achieve improvedpower saving. Such broadcast and multicast traffic may include trafficassociated with managing network connectivity, network monitoring, etc.The access point may send (i) a Delivery Traffic Indication Message(DTIM) to indicate regular broadcast and multicast traffic being sent bythe access point and (ii) a slow DTIM to indicate broadcast andmulticast traffic of potential interest to the PS-stations. The slowDTIM may be sent at a slower rate than the DTIM. The PS-stations maylisten for the slow DTIM and may sleep through the DTIM.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless network with an access point and multiplestations.

FIG. 2 shows an example transmission timeline for the access point.

FIG. 3 shows a design of a beacon frame.

FIG. 4 shows a process for negotiating a listen interval.

FIG. 5 shows an apparatus for negotiating a listen interval.

FIG. 6 shows a process for renegotiating the listen interval on the fly.

FIG. 7 shows an apparatus for renegotiating the listen interval on thefly.

FIG. 8 shows a process for avoiding association time out.

FIG. 9 shows an apparatus for avoiding association time out.

FIG. 10 shows a process for receiving broadcast and multicast traffic inthe power-save mode.

FIG. 11 shows an apparatus for receiving broadcast and multicast trafficin the power-save mode.

FIG. 12 shows a block diagram of an access point and a station.

DETAILED DESCRIPTION

The power saving techniques described herein may be used for variouswireless networks such as WLANs, WMANs, WWANs, WPANs, etc. A WLAN mayimplement a radio technology such as any defined by IEEE 802.11,Hiperlan, etc. A WWAN may be a cellular network such as a Code DivisionMultiple Access (CDMA) network, a Time Division Multiple Access (TDMA)network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal FDMA (OFDMA) network, a Single-Carrier FDMA (SC-FDMA)network, etc. A WMAN may implement a radio technology such as anydefined by IEEE 802.16 such as 802.16e, which is commonly referred to asWiMAX, or IEEE 802.20. A WPAN may implement a radio technology such asBluetooth. For clarity, the techniques are described below for an IEEE802.11 WLAN.

FIG. 1 shows a wireless network 100 with an access point (AP) 110 andmultiple stations (STAs) 120. In general, a wireless network may includeany number of access points and any number of stations. A station is adevice that can communicate with another station via a wireless medium.The terms “wireless medium” and “channel” are often usedinterchangeably. A station may communicate with an access point orpeer-to-peer with another station. A station may also be called, and maycontain some or all of the functionality of, a terminal, a mobilestation, a user equipment, a subscriber unit, etc. A station may be acellular phone, a handheld device, a wireless device, a personal digitalassistant (PDA), a laptop computer, a wireless modem, a cordless phone,etc. An access point is a station that provides access to distributionservices via the wireless medium for stations associated with thataccess point. An access point may also be called, and may contain someor all of the functionality of, a base station, a base transceiverstation (BTS), a Node B, an evolved Node B (eNode B), etc.

For a centralized network, a network controller 130 couples to theaccess points and provides coordination and control for these accesspoints. Network controller 130 may be a single network entity or acollection of network entities. For a distributed network, the accesspoints may communicate with one another as needed without the uses ofnetwork controller 130.

Wireless network 100 may implement the IEEE 802.11 family of standards.For example, wireless network 100 may implement IEEE 802.11, 802.11a,802.11b, 802.11e and/or 802.11g, which are existing IEEE 802.11standards. Wireless network 100 may also implement IEEE 802.11n and/or802.11s, which are IEEE 802.11 standards being formed. IEEE 802.11,802.11a, 802.11b, 802.11g and 802.11n cover different radio technologiesand have different capabilities. IEEE 802.11e covers quality of service(QoS) enhancements for a Medium Access Control (MAC) layer. In IEEE802.11e, a station that supports QoS facility is referred to as QSTA,and an access point that supports QoS facility is referred to as QAP.QoS facility refers to mechanisms used to provide parameterized andprioritized QoS.

A station may communicate with an access point for one or more flows. Aflow is a higher layer data stream that is sent via a link. A flow mayutilize Transmission Control Protocol (TCP), User Datagram Protocol(UDP), or some other protocol at a transport layer. A flow may also bereferred to as a data stream, a traffic stream, etc. A flow may carryany type of data such as voice, video, packet data, etc. A flow may befor a particular traffic class and may have certain requirements on datarate, latency or delay, etc. A flow may be (a) periodic and sent atregular intervals or (b) non-periodic and sent sporadically, e.g.,whenever there is data to send. A periodic flow is a flow in which datais sent at regular intervals. For example, a flow for VoIP may send adata frame every 10 or 20 milliseconds (ms). As used herein, a frame isa unit of transmission and may be a data frame, a null frame, a controlframe, or some other type of frame. A frame may also be referred to as apacket, a data block, a data unit, a protocol data unit (PDU), a servicedata unit (SDU), a MAC PDU (MPDU), etc. A call for a station may haveone or more flows for one or more traffic types.

FIG. 2 shows an example transmission timeline 200 for access point 110in wireless network 100. In general, each access point in a wirelessnetwork may maintain a separate timeline for all transmissions coveredby that access point. The transmission timeline for access point 110 isdescribed below. Access point 110 periodically transmits a beacon on thedownlink. This beacon carries a preamble and an access point identifier(AP ID) that allows the stations to detect and identify the accesspoint. The time interval between the start of two consecutive beacons iscalled a target beacon transmit time (TBTT) or a beacon interval. Thebeacon interval may be fixed or variable and may be set to a suitableduration, e.g., 100 ms.

Each beacon interval may include any number of service periods for anynumber of stations. A service period is a contiguous time durationduring which an access point may transmit one or more downlink frames toa station and/or may grant one or more transmission opportunities(TXOPs) to the same station. A TXOP is an allocation of time fortransmission on a link. A service period may be scheduled orunscheduled. A given station may have any number of service periodswithin a given beacon interval.

A station typically performs association procedures to associate with anaccess point when the station is first powered up or moves into a newWLAN coverage area. Association refers to the mapping of a station to anaccess point, which enables the station to receive distribution service.The association allows the distribution service to know which accesspoint to contact for the station. The station attempts to disassociatewhenever it leaves the network. The station performs reassociationprocedures to “move” a current association from one access point toanother access point. The association, disassociation, and reassociationprocedures are described in IEEE 802.11 documents.

A station typically performs negotiation with an access point forvarious features or attributes such as security, Internet Protocol (IP)address, QoS, flows, power management, etc. The negotiation typicallyentails exchanging request and response frames between the station andthe access point until pertinent parameter values are agreed uponbetween the station and the access point. Thereafter, the stationoperates in accordance with the states or context defined by theparameters negotiated with the access point.

IEEE 802.11 defines a power-save (PS) mode for stations desiring toconserve battery power. A station that desires to operate in thepower-save mode indicates this intention to an access point by setting a“PS-mode” bit to 1 in a MAC header of a transmission sent to the accesspoint. A station that is in the power-save mode is referred to as aPS-station. In response, the access point recognizes that the stationwill be sleeping and will wake up only at agreed upon times to receivetraffic. The access point then buffers any incoming traffic data for thestation and delivers the data to the station when the station is awake.

A station that is in the power-save mode may choose to wake up toreceive a Traffic Indication Map (TIM) and/or a Delivery TrafficIndication Message (DTIM). The TIM is a bitmap that is present in everybeacon transmitted by an access point. The TIM in a given beaconindicates to the station whether there is pending unicast traffic forthat station in the upcoming beacon interval. At the time ofassociation, the station and the access point negotiate a listeninterval that indicates how often the station will wake up to listen forbeacon and hence receive the TIM. The listen interval is typicallymultiple times the beacon interval, as shown in FIG. 2. For example, ifthe station has a listen interval of five, then the station may wake upat every fifth beacon to decode the TIM and receive potential trafficfor that station.

The DTIM is a bitmap that indicates whether broadcast and multicasttraffic is being delivered in the upcoming beacon interval. The DTIM issent at an interval that is selected by the access point. The DTIMinterval is typically multiple times the beacon interval and is fixedfor a Basic Service Set (BSS), which is a network of stations associatedto the access point. A station that is willing to receive broadcast ormulticast traffic would decode the DTIM independently of the listeninterval for that station.

An access point may select a DTIM interval based on a tradeoff betweenlatency, buffer size requirements, and power saving. Similarly, astation that is in the power-save mode may select a listen interval aswell as whether or not to wake for the DTIM based on a tradeoff betweenlatency, buffer size requirements, and power saving.

In general, a longer listen interval provides more power saving for astation in the power-save mode but results in more delay, which may betolerable for some types of traffic. Hence, the station may request alarge listen interval at the time of association with an access point ifthe station favors power saving. However, a larger listen intervalresults in larger buffer size requirements for the access point to storepotential incoming traffic for all stations supported by that accesspoint. Supporting a large listen interval is thus a constraint for theaccess point because the buffers used for storing potential incomingtraffic should be sized according to the amount of data that might bereceived during the listen interval for all stations supported by theaccess point.

IEEE 802.11 does not impose a requirement on the maximum listen intervalthat an access point needs to support. An access point may supportlisten intervals within a particular range, e.g., from 1 to 20 times thebeacon interval, or possibly more. The supported listen interval rangemay be dependent on various factors such as the capability of the accesspoint, the number of stations being served by the access point, thenumber of stations in the power-save mode, etc. Different access pointsfrom different vendors may support different ranges of listen intervals.Furthermore, the maximum listen interval supported by a given accesspoint may change over time, e.g., depending on the number of stationsthat are in the power-save mode with that access point. Conventionally,a station has no easy way of knowing the maximum listen intervalsupported by an access point.

In an aspect, an access point conveys the maximum listen intervalsupported by that access point, and a station uses this information tomore efficiently select a suitable listen interval. In one design, theaccess point advertises the maximum listen interval in the beacon. Abeacon frame includes various information elements carrying varioustypes of information. An information element may be defined for maximumlisten interval and may be included in a beacon frame sent by the accesspoint.

FIG. 3 shows a design of a beacon frame 300 that may be transmitted byan access point. Beacon frame 300 includes a Timestamp field thatindicates the timing of the access point, a Beacon Interval field thatindicates the time duration between beacons, a Capability Informationfield that indicates the requested or advertised capabilities of theaccess point, a Service Set Identity (SSID) field that carries anidentifier for the WLAN, and other information elements defined by IEEE802.11. In the design shown in FIG. 3, beacon frame 300 includes aMaximum Listen Interval information element 310. Information element 310includes an Element ID field 312 that is set to a unique value assignedto information element 310, a Length field 314 that indicates the lengthof subsequent field 316, and field 316 that carries the maximum listeninterval supported by the access point.

A station may listen for a beacon frame upon power up or moving into anew WLAN coverage area. The station may then determine the maximumlisten interval supported by the access point. If the station desires tomaximize its power saving, then the station may select the maximumlisten interval advertised by the access point. The station may alsoselect a shorter listen interval based on its traffic requirements. Inany case, the station is able to select and include a suitable listeninterval in the first association request sent to the access point.

In another design, an access point conveys the maximum listen intervalthat it supports in a unicast frame sent to a station. An informationelement may be defined for maximum listen interval and may be includedin a frame sent by the access point to the station. In one scheme, themaximum listen interval is conveyed during system access. A station maysend a probe request to an access point. The access point may includethe maximum listen interval supported by that access point in a proberesponse sent to the station, e.g., if the “PS-mode” bit is set to 1. Inanother scheme, the maximum listen interval is conveyed duringassociation. A station may select a listen interval desired by thestation and include the selected listen interval in the firstassociation request sent to the access point. If the selected serviceinterval is not supported by the access point, then the access point maysend an association response that includes the maximum listen intervalsupported by the access point. The station may then select a suitablelisten interval and include it in the next association request.

An access point may also convey the maximum listen interval supported bythat access point in other manners. A station may determine the maximumlisten interval based on a beacon, a probe response, an associationresponse, or some other transmission. The station may then select asuitable listen interval without or with little guesswork and may savepower in the association procedure.

FIG. 4 shows a process 400 for negotiating a listen interval. A stationinitially determines a maximum listen interval supported by an accesspoint (block 412). The station may obtain the maximum listen intervalfrom a beacon, a control frame sent in a probe response or anassociation response, or some other transmission sent by the accesspoint. The station then selects a listen interval based on the maximumlisten interval (block 414). For example, the selected listen intervalmay be equal to the maximum listen interval if the station desires tomaximize power saving and its traffic can tolerate the delay. Thestation then sends the selected listen interval to the access point(block 416).

FIG. 5 shows a design of an apparatus 500 for negotiating a listeninterval. Apparatus 500 includes means for determining a maximum listeninterval supported by an access point (module 512), means for selectinga listen interval based on the maximum listen interval (module 514), andmeans for sending the selected listen interval to the access point(module 516). Modules 512 to 516 may comprise processors, electronicsdevices, hardware devices, electronics components, logical circuits,memories, etc., or any combination thereof.

A station may also determine the maximum listen interval supported by anaccess point in other manners. The station may send one or more requeststo determine the maximum listen interval supported by the access point.If a large listen interval is desired, then the station may try one ormore listen intervals at association time until the access point acceptsone of the listen intervals. The station may request the largest listeninterval in the first association request sent to the access point. Ifthe requested listen interval is too large, then the access point maysimply respond with an error status code in an association response,e.g., a status code of 51 for “Association denied because the listeninterval is too large”. The status code in the response does not conveyto the station the largest listen interval supported by the accesspoint. Hence, the station may then request a smaller listen interval inthe next association request sent to the access point. The station mayrequest progressively smaller listen intervals until a requested listeninterval is within the range supported by the access point.

The station may also send the requests for listen intervals in otherorders. For example, the station may send a request for a listeninterval of N. If that listen interval is supported, then the stationmay send a request for a larger listen interval, e.g., N+1. Otherwise,the station may send a request for a smaller listen interval, e.g., N−1.The station may repeat sending requests until the maximum listeninterval is discovered and may then use it.

In general, a station may determine the maximum listen intervalsupported by an access point in a heuristic manner. The station may sendmultiple requests for multiple listen interval values until the stationreceives a response accepting one of the requests and another responsedenying another one of the requests. The station may send one requestfor one listen interval value at a time. The station may start with arequest for a largest listen interval value and conclude with a requestfor a smallest listen interval value, until the response accepting oneof the requests is received. The station may also start with a requestfor a smallest listen interval value and conclude with a request for alargest listen interval value, until the response denying one of therequests is received. The station may also start with a request for amiddle listen interval value, send a request for a larger listeninterval value if a response accepting the request is received, and senda request for a smaller listen interval value if a response denying therequest is received. The station may also send the requests in otherorders. The station may determine a suitable listen interval for usebased on the received responses.

A station typically negotiates an appropriate listen interval when itassociates with an access point. The station thereafter uses thenegotiated listen interval for the entire duration of the associationwith the access point. The negotiated listen interval may be inadequateor undesirable for various reasons, and the station may desire to selecta more suitable listen interval. In this case, the station woulddisassociate with the access point and then reassociate with the sameaccess point. The station may negotiate a more suitable listen intervalduring the reassociation with the access point. The current IEEE 802.11standard does not provide a mechanism for updating the listen intervalwhile a station is associated with an access point.

In another aspect, a station renegotiates the listen interval on the flywithout having to disassociate and reassociate with an access point.This capability may provide certain advantages, as described below.

FIG. 6 shows a process 600 for a station to renegotiate the listeninterval on the fly. The station initially establishes an associationwith an access point (block 612). The station negotiates a first listeninterval and establishes states or context (e.g., for security, IPaddress, QoS, power management, etc.) during establishment of theassociation (block 614). The station thereafter receives data based onthe first listen interval and the established states (block 616).

The station thereafter determines that the first listen interval isinsufficient for whatever reason. The station then renegotiates with theaccess point for a second listen interval without disassociating withthe access point (block 618). The second listen interval may be shorteror longer than the first listen interval, depending on the requirementsof the station. The station may select the second listen interval withor without knowledge of the maximum listen interval supported by theaccess point. For the renegotiation, the station may send to the accesspoint a control frame with the second listen interval. The access pointmay grant or deny the request by the station. If the request is granted,then the access point may send a response (e.g., an acknowledgement)indicating that the request is granted. The station receives theresponse and thereafter receives data based on the second listeninterval (block 620). If the access point denies the second listeninterval, then the station and the access point may continue negotiationuntil a suitable listen interval is selected and accepted.

In one design, the states or context (e.g., for security, IP address,QoS, power management, etc.) are retained for the station, and only thelisten interval is changed during the renegotiation. In this design, thestation thereafter communicates with the access point based on thestates/context established earlier during association establishment(block 622). In another design, one or more parameters may also berenegotiated and modified either in the control frame carrying thesecond listen interval sent by the station or in one or more subsequentframes.

FIG. 7 shows a design of an apparatus 700 for renegotiating the listeninterval on the fly. Apparatus 700 includes means for establishing anassociation with an access point (module 712), means for negotiating afirst listen interval and establishing states or context duringestablishment of the association (module 714), means for receiving databased on the first listen interval and the established states (module716), means for renegotiating with the access point for a second listeninterval without disassociating with the access point (module 718),means for receiving data based on the second listen interval (module720), and means for communicating with the access point based on thestates/context established earlier during association establishment(module 722). Modules 712 to 722 may comprise processors, electronicsdevices, hardware devices, electronics components, logical circuits,memories, etc., or any combination thereof.

In one design, new frames that are not currently in IEEE 802.11 aredefined and used for sending a request for a new listen interval and aresponse to this request. In another design, new information elementsare defined and included in existing frames to request for a new listeninterval and to respond to the request.

A station may be dormant for an extended duration that is longer thanthe maximum listen interval supported by an access point. In this case,entities operating above Layer 2 in the network may buffer traffic forthe station and synchronize delivery from a page buffering function(PBF) to the station. The traffic buffering may thus occur upstream ofthe access point. The PBF may be synchronized with the station and maysend traffic for the station such that the traffic reaches the accesspoint shortly before the station wakes up at the start of the nextlisten interval and decodes the TIM in the beacon. The access point doesnot need to be aware of the extended dormancy by the station. The accesspoint may operate in a normal manner as if the station is waking upevery listen interval to decode the TIM. However, the station may wakeup at a multiple of the listen interval, which is synchronized with thePBF. The longer actual listen interval may allow the station to savemore power. The PBF may ensure that traffic is sent when the station isawake to receive it.

When a station wakes up at a rate that is less frequent than the listeninterval and an access point does not have this knowledge, there is arisk that the access point may disassociate the station if the accesspoint does not detect any activity from the station for an extendedperiod of time. If the access point disassociates the station, then thestates/context for the station may be lost. The station may need toperform reassociation procedures in order to re-establish thestates/context with the access point. This is undesirable since thereassociation procedures consume time and power.

In yet another aspect, an access point conveys its association timeoutto the stations, and a station may use this information to avoid beingtimed out by the access point. In one design, the access pointadvertises its association timeout in the beacon. Referring to thedesign shown in FIG. 3, beacon frame 300 includes an Association Timeoutinformation element 320 that includes the association timeout for theaccess point. The access point may set this information element to thecurrent value of the association timeout used by the access point. Inanother design, the access point conveys the association timeout in aunicast frame, e.g., for a probe response or an association response.

A station that is dormant for longer than the negotiated listen intervalwith an access point may obtain the association timeout of the accesspoint. The station may then ensure to be active at least once in everyassociation timeout in order to keep the association with the accesspoint alive. Correspondingly, the access point may ensure to keep thestation associated for at least the advertised association timeoutduration, even when the station shows no activity.

FIG. 8 shows a process 800 for a station to avoid association time out,e.g., due to extended dormancy. The station initially establishes anassociation with an access point (block 812). The station determines anassociation timeout for the access point, e.g., based on a beacon or aframe sent by the access point (block 814). The station may negotiatewith the access point for a listen interval during establishment of theassociation. The station may sleep for a period longer than the listeninterval, possibly without informing the access point (block 816). Thestation becomes active at least once in every association timeout tokeep the association with the access point alive (block 818).

FIG. 9 shows a design of an apparatus 900 for avoiding association timeout. Apparatus 900 includes means for establishing an association withan access point (module 912), means for determining an associationtimeout for the access point, e.g., based on a beacon or a frame sent bythe access point (module 914), means for sleeping for a period longerthan a listen interval negotiated during establishment of theassociation, possibly without informing the access point (module 916),and means for becoming active at least once in every association timeoutto keep the association with the access point alive (module 918).Modules 912 to 918 may comprise processors, electronics devices,hardware devices, electronics components, logical circuits, memories,etc., or any combination thereof.

An access point may advertise the maximum listen interval and/or theassociation timeout supported by that access point in the beacon, asdescribed above. The maximum listen interval and/or the associationtimeout may be received by, and applied to, all stations within thecoverage of the access point. The access point may also convey themaximum listen interval and/or the association timeout in unicast framessent to specific stations. The access point may use different maximumlisten intervals and/or different association timeouts for differentstations, different access categories, etc. For example, a longer listeninterval and/or a longer association timeout may be used for a stationwith higher priority. Conversely, a shorter listen interval and/or ashorter association timeout may be used for a station with lowerpriority. Individual listen interval and/or association timeout for aspecific station may be conveyed in the beacon or unicast frames.

The current IEEE 802.11 standard supports power save for a station andgroups traffic into two categories:

-   -   Broadcast and multicast traffic indicated by the DTIM, and    -   Unicast traffic sent in directed frames to the station after the        presence of the traffic is indicated in the beacon's TIM at        every listen interval.

A station may desire to receive broadcast or multicast traffic (e.g.,audio, streaming video, etc.) from an application layer. The station maythen wake up a sufficient amount of time in order to receive thesetraffic streams. The station is likely not a candidate for deep sleepand significant power-save operation because the DTIM may be sent often,e.g., every beacon.

Conventionally, the broadcast and multicast traffic indicated by theDTIM includes (1) broadcast and multicast traffic from the applicationlayer, which is referred to herein as “application” broadcast andmulticast traffic, and (2) broadcast and multicast traffic associatedwith managing network connectivity, network monitoring, etc., which isreferred to herein as “network” broadcast and multicast traffic. Someexamples of network broadcast and multicast traffic include AddressResolution Protocol (ARP) traffic, Dynamic Host Configuration Protocol(DHCP) traffic, topology updates, and other such types of traffic. ARPis used to map MAC addresses to IP addresses. DHCP is used for dynamicIP configuration. A station may desire to receive network broadcast andmulticast traffic even when the station intends to be idle and operatingin deep sleep.

Conventionally, both application and network broadcast and multicasttraffic are included together and sent using the DTIM mechanism. An idlestation that desires to save power will likely not be interested inreceiving the application broadcast and multicast traffic. Otherwise,the station may have its display, keypad, and processor turned on, andtherefore may not be saving much power anyway. However, the idleterminal may desire to ensure that its connectivity for Layer 2 andabove is operational. For example, the station may desire to respond toARP requests, possible DHCP messages, etc. These messages are alsobroadcast traffic and are thus sent using the DTIM.

The DTIM indicates both (a) network broadcast and multicast traffic usedto maintain Layer 2 and above connectivity and (b) application broadcastand multicast traffic. Hence, a station that is interested in receivingonly network broadcast and multicast traffic would need to wake up foreach DTIM in order to receive potential network broadcast and multicasttraffic. The DTIM is typically sent in every beacon (or every fewbeacons) in order to reduce the delay of the application broadcast andmulticast traffic. In this case, the station may need to wake up at eachbeacon for the DTIM, which may severely impact power save performance.

In yet another aspect, an access point sends network broadcast andmulticast traffic in a manner to improve power saving for stations inthe power-save mode. A new service access point (SAP) may be madeavailable for a new broadcast and multicast traffic class that isassociated with stations in the power-save mode. This traffic class maybe referred to as Power Save (PS) broadcast and multicast traffic andmay include network broadcast and multicast traffic and/or otherbroadcast and multicast traffic that might be of interest to stations inthe power-save mode.

A new DTIM may also be made available and may be referred to as aSlowDTIM or slow DTIM. The PS broadcast and multicast traffic may besent using the SlowDTIM. The SlowDTIM may be sent at every SlowDTIMinterval, which is a predetermined number of beacon intervals. TheSlowDTIM interval may be larger than the DTIM interval and may beselected based on a tradeoff between power saving and messaging delay.For example, the SlowDTIM may be sent in every 2, 3, 4, or some othermultiple of the DTIM.

Traffic relevant to maintaining Layer 2 and above connectivity and/orother types of PS broadcast and multicast traffic may be sent using theSlowDTIM. The PS broadcast and multicast traffic may also be copied andsent using the DTIM so that stations that do not receive the SlowDTIMcan also receive this traffic. Application broadcast and multicasttraffic is not sent using the SlowDTIM and is instead sent using theDTIM.

A station in the power-save mode may be able to maintain Layer 2 andabove connectivity by listening to the SlowDTIM and receiving networkbroadcast and multicast traffic used to maintain network connectivity.The station may sleep through the DTIM, which may be sent at a shorterinterval or a faster rate. The SlowDTIM may improve power saving for thestation.

In one design, the SlowDTIM is sent every N DTIM, where N may be anyinteger greater than one. In this design, a station in the power-savemode may wake up at each listen interval as well as for each SlowDTIM.In another design, the SlowDTIM is sent in a manner to reduce the numberof times that power-save stations need to wake up. For example, theSlowDTIM may be sent in each listen interval for a station or a group ofstations having the same listen interval. A station may then receive theSlowDTIM and the TIM from the same beacon in each listen interval.

A station may desire deep sleep and may select a listen interval that ismuch longer than the SlowDTIM interval. In one design, to avoidrequiring the station to wake up at each SlowDTIM interval, the networkbroadcast and multicast traffic may be sent directly to the station inunicast frames. The station may then receive the network broadcast andmulticast traffic when the station wakes up for its listen interval. Thestation and the access point may configure this mode of trafficdelivery, e.g., during configuration setup for the power-save mode. Thistraffic delivery mode may be selectively applied to stations desiringdeep sleep and may be readily supported by the access point when thenetwork broadcast and multicast traffic is segregated from theapplication broadcast and multicast traffic.

FIG. 10 shows a process 1000 for receiving broadcast and multicasttraffic by a station in the power-save mode. The station receives a slowDTIM sent at a slower rate than a regular DTIM, with the regular DTIMindicating first broadcast and multicast traffic and the slow DTIMindicating second broadcast and multicast traffic. (block 1012). Thefirst broadcast and multicast traffic may comprise network broadcast andmulticast traffic, application broadcast and multicast traffic, and/orother broadcast and multicast traffic for a WLAN. The second broadcastand multicast traffic may comprise network broadcast and multicasttraffic and/or other broadcast and multicast traffic that might beinterest to stations in the power-save mode. The station receives thesecond broadcast and multicast traffic (e.g., used for maintainingnetwork connectivity) as indicated by the slow DTIM (block 1014). Theslow DTIM may be sent in every N regular DTIM, in every listen intervalfor the station, etc. The station may sleep through the regular DTIM(block 1016).

FIG. 11 shows a design of an apparatus 1100 for receiving broadcast andmulticast traffic in the power-save mode. Apparatus 1100 includes meansfor receiving a slow DTIM sent at a slower rate than a regular DTIM,with the regular DTIM indicating first broadcast and multicast trafficand the slow DTIM indicating second broadcast and multicast traffic(module 1112), means for receiving the second broadcast and multicasttraffic (e.g., used for maintaining network connectivity), as indicatedby the slow DTIM (module 1114), and means for sleeping through theregular DTIM (module 1116). Modules 1112 to 1116 may compriseprocessors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

FIG. 12 shows a block diagram of access point 110 and station 120, whichmay be one of the stations in FIG. 1. On the downlink, at access point110, a transmit (TX) data processor 1212 receives traffic data from adata source 1210 for the stations scheduled for transmission, controldata (e.g., the maximum listen interval, association timeout, responseframes, etc.) from a controller/processor 1220, and schedulinginformation (e.g., TIM, DTIM, slow DTIM, etc.) from a scheduler 1224 viacontroller/processor 1220. TX data processor 1212 processes (e.g.,encodes, interleaves, modulates, and scrambles) the traffic data foreach station based on a rate selected for that station, processes thecontrol data and scheduling information, and generates data chips. Atransmitter (TMTR) 1214 processes (e.g., converts to analog, amplifies,filters, and upconverts) the data chips and generates a downlink signal,which is transmitted via an antenna 1216 to the stations.

At station 120, an antenna 1252 receives the downlink signal from accesspoint 110 and provides a received signal. A receiver (RCVR) 1254processes the received signal and provides samples. A receive (RX) dataprocessor 1256 processes (e.g., descrambles, demodulates, deinterleaves,and decodes) the samples, provides decoded data for station 120 to adata sink 1258, and provides control data and scheduling information toa controller/processor 1260.

On the uplink, at station 120, a TX data processor 1272 receives trafficdata from a data source 1270 and control data (e.g., listen interval,request frames, etc.) from controller/processor 1260. TX data processor1272 processes the traffic and control data based on a rate selected forthe station and generates data chips. A transmitter 1274 processes thedata chips and generates an uplink signal, which is transmitted viaantenna 1252 to access point 110.

At access point 110, antenna 1216 receives the uplink signals from thestation 120 and other stations. A receiver 1230 processes a receivedsignal from antenna 1216 and provides samples. An RX data processor 1232processes the samples and provides decoded data for each station to adata sink 1234 and provides control data to controller/processor 1220.

Controllers/processors 1220 and 1260 direct operation at access point110 and station 120, respectively. Scheduler 1224 may perform schedulingfor the stations and may also perform scheduling for broadcast andmulticast traffic sent using the DTIM and slow DTIM. Scheduler 1224 mayreside at access point 110, as shown in FIG. 12, or at another networkentity.

The power saving techniques described herein may be implemented byvarious means. For example, these techniques may be implemented inhardware, firmware, software, or a combination thereof. For a hardwareimplementation, the processing units used to perform the techniques at astation may be implemented within one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, electronic devices, other electronicunits designed to perform the functions described herein, or acombination thereof. The processing units used to perform the techniquesat an access point may be implemented within one or more ASICs, DSPs,processors, etc.

For a firmware and/or software implementation, the power savingtechniques may be implemented with modules (e.g., procedures, functions,etc.) that perform the functions described herein. The firmware and/orsoftware codes may be stored in a memory (e.g., memory 1222 or 1262 inFIG. 12) and executed by a processor (e.g., processor 1220 or 1260). Thememory may be implemented within the processor or external to theprocessor.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

1. An apparatus comprising: a processor configured to determine amaximum listen interval supported by an access point, to select a listeninterval based on the maximum listen interval, and to send the selectedlisten interval to the access point; and a memory coupled to theprocessor.
 2. The apparatus of claim 1, wherein the processor isconfigured to receive a beacon sent by the access point and to obtainthe maximum listen interval from the beacon.
 3. The apparatus of claim1, wherein the processor is configured to send a probe request to theaccess point and to receive a probe response with the maximum listeninterval from the access point.
 4. The apparatus of claim 1, wherein theprocessor is configured to select an initial listen interval, to send anassociation request with the initial listen interval to the accesspoint, and to receive an association response with the maximum listeninterval from the access point.
 5. The apparatus of claim 1, wherein theprocessor is configured to receive data from the access point at timeinstances determined based on the selected listen interval and to sleepbetween the time instances.
 6. The apparatus of claim 1, wherein theselected listen interval is equal to the maximum listen interval.
 7. Amethod comprising: determining a maximum listen interval supported by anaccess point; selecting a listen interval based on the maximum listeninterval; and sending the selected listen interval to the access point.8. The method of claim 7, wherein the determining the maximum listeninterval comprises receiving a beacon sent by the access point, andobtaining the maximum listen interval from the beacon.
 9. The method ofclaim 7, further comprising: receiving data from the access point attime instances determined based on the selected listen interval andsleeping between the time instances.
 10. An apparatus comprising: meansfor determining a maximum listen interval supported by an access point;means for selecting a listen interval based on the maximum listeninterval; and means for sending the selected listen interval to theaccess point.
 11. A processor-readable medium including instructionsstored thereon, comprising: a first instruction set for determining amaximum listen interval supported by an access point; a secondinstruction set for selecting a listen interval based on the maximumlisten interval; and a third instruction set for sending the selectedlisten interval to the access point.
 12. An apparatus comprising: aprocessor configured to send a plurality of requests for a plurality oflisten interval values, to receive a response accepting one of theplurality of requests, to receive another response denying another oneof the plurality of requests, and to determine a listen interval for usebased on the received responses; and a memory coupled to the processor.13. The apparatus of claim 12, wherein the processor is configured tosend one request for one listen interval value at a time until theresponse accepting one of the plurality of requests and the responsedenying another one of the plurality of requests are both received. 14.The apparatus of claim 12, wherein the processor is configured to sendone request for one listen interval value at a time, starting with arequest for a largest listen interval value and concluding with arequest for a smallest listen interval value, until the responseaccepting one of the plurality of requests is received.
 15. Theapparatus of claim 12, wherein the processor is configured to send onerequest for one listen interval value at a time, starting with a requestfor a smallest listen interval value and concluding with a request for alargest listen interval value, until the response denying another one ofthe plurality of requests is received.
 16. An apparatus comprising: aprocessor configured to send a maximum listen interval supported by anaccess point, to receive from a station a listen interval selected basedon the maximum listen interval, and to send data to the station based onthe listen interval; and a memory coupled to the processor.
 17. Theapparatus of claim 16, wherein the processor is configured to send themaximum listen interval in a beacon or a frame to the station.
 18. Anapparatus comprising: a processor configured to establish an associationwith an access point, to receive data based on a first listen intervalnegotiated with the access point during establishment of theassociation, to renegotiate with the access point for a second listeninterval without disassociating with the access point, and to receivedata based on the second listen interval after the renegotiation; and amemory coupled to the processor.
 19. The apparatus of claim 18, whereinthe processor is configured to establish states during the establishmentof the association and to retain the states during the renegotiation forthe second listen interval.
 20. The apparatus of claim 18, wherein theprocessor is configured to send a control frame with the second listeninterval to the access point and to receive an indication of acceptanceof the second listen interval from the access point.
 21. The apparatusof claim 18, wherein the processor is configured to wake up for beaconframes determined by the first or second listen interval and to sleepbetween the beacon frames when no data is sent to the apparatus.
 22. Amethod comprising: establishing an association with an access point;receiving data based on a first listen interval negotiated with theaccess point during establishment of the association; renegotiating withthe access point for a second listen interval without disassociatingwith the access point; and receiving data based on the second listeninterval after the renegotiation.
 23. The method of claim 22, furthercomprising: establishing states during establishment of the association;and retaining the states during the renegotiation for the second listeninterval.
 24. An apparatus comprising: means for establishing anassociation with an access point; means for receiving data based on afirst listen interval negotiated with the access point duringestablishment of the association; means for renegotiating with theaccess point for a second listen interval without disassociating withthe access point; and means for receiving data based on the secondlisten interval after the renegotiation.
 25. A processor-readable mediumincluding instructions stored thereon, comprising: a first instructionset for establishing an association with an access point; a secondinstruction set for receiving data based on a first listen intervalnegotiated with the access point during establishment of theassociation; a third instruction set for renegotiating with the accesspoint for a second listen interval without disassociating with theaccess point; and a fourth instruction set for receiving data based onthe second listen interval after the renegotiation.
 26. An apparatuscomprising: a processor configured to establish an association for astation, to send data to the station based on a first listen intervalnegotiated with the station during establishment of the association, torenegotiate with the station for a second listen interval withoutdisassociating the station, and to send data to the station based on thesecond listen interval after the renegotiation; and a memory coupled tothe processor.
 27. The apparatus of claim 26, wherein the processor isconfigured to establish states for the station during the establishmentof the association and to retain the states for the station during therenegotiation for the second listen interval.
 28. An apparatuscomprising: a processor configured to establish an association with anaccess point, to determine an association timeout for the access point,and to become active at least once in every association timeout to keepthe association with the access point alive; and a memory coupled to theprocessor.
 29. The apparatus of claim 28, wherein the processor isconfigured to receive a beacon sent by the access point and to obtainthe association timeout from the beacon.
 30. The apparatus of claim 28,wherein the processor is configured to receive a frame from the accesspoint and to obtain the association timeout from the received frame. 31.The apparatus of claim 28, wherein the processor is configured tonegotiate with the access point for a listen interval during theestablishment of the association and to sleep for a period longer thanthe listen interval.
 32. The apparatus of claim 28, wherein theprocessor is configured to negotiate with the access point for a listeninterval during the establishment of the association and to sleep for aperiod longer than the listen interval without informing the accesspoint.
 33. A method comprising: establishing an association with anaccess point; determining an association timeout for the access point;and becoming active at least once in every association timeout to keepthe association with the access point alive.
 34. The method of claim 33,wherein the determining the association timeout comprises receiving abeacon sent by the access point, and obtaining the association timeoutfrom the beacon.
 35. The method of claim 33, further comprising:negotiating with the access point for a listen interval during theestablishment of the association; and sleeping for a period longer thanthe listen interval.
 36. An apparatus comprising: means for establishingan association with an access point; means for determining anassociation timeout for the access point; and means for becoming activeat least once in every association timeout to keep the association withthe access point alive.
 37. A processor-readable medium includinginstructions stored thereon, comprising: a first instruction set forestablishing an association with an access point; a second instructionset for determining an association timeout for the access point; and athird instruction set for becoming active at least once in everyassociation timeout to keep the association with the access point alive.38. An apparatus comprising: a processor configured to establish anassociation for a station, to send an association timeout supported byan access point, and to receive from the station at least onetransmission in every association timeout to keep the association alive;and a memory coupled to the processor.
 39. The apparatus of claim 38,wherein the processor is configured to send the association timeout in abeacon or a frame to the station.